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// This file is part of Substrate.

// Copyright (C) 2019-2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Traits and associated utilities for scheduling dispatchables in FRAME.

use codec::{Codec, Decode, Encode, EncodeLike};
use sp_runtime::{DispatchError, RuntimeDebug};
use sp_std::{fmt::Debug, prelude::*};

/// Information relating to the period of a scheduled task. First item is the length of the
/// period and the second is the number of times it should be executed in total before the task
/// is considered finished and removed.
pub type Period<BlockNumber> = (BlockNumber, u32);

/// Priority with which a call is scheduled. It's just a linear amount with lowest values meaning
/// higher priority.
pub type Priority = u8;

/// The dispatch time of a scheduled task.
#[derive(Encode, Decode, Copy, Clone, PartialEq, Eq, RuntimeDebug)]
pub enum DispatchTime<BlockNumber> {
	/// At specified block.
	At(BlockNumber),
	/// After specified number of blocks.
	After(BlockNumber),
}

/// The highest priority. We invert the value so that normal sorting will place the highest
/// priority at the beginning of the list.
pub const HIGHEST_PRIORITY: Priority = 0;
/// Anything of this value or lower will definitely be scheduled on the block that they ask for, even
/// if it breaches the `MaximumWeight` limitation.
pub const HARD_DEADLINE: Priority = 63;
/// The lowest priority. Most stuff should be around here.
pub const LOWEST_PRIORITY: Priority = 255;

/// A type that can be used as a scheduler.
pub trait Anon<BlockNumber, Call, Origin> {
	/// An address which can be used for removing a scheduled task.
	type Address: Codec + Clone + Eq + EncodeLike + Debug;

	/// Schedule a dispatch to happen at the beginning of some block in the future.
	///
	/// This is not named.
	fn schedule(
		when: DispatchTime<BlockNumber>,
		maybe_periodic: Option<Period<BlockNumber>>,
		priority: Priority,
		origin: Origin,
		call: Call,
	) -> Result<Self::Address, DispatchError>;

	/// Cancel a scheduled task. If periodic, then it will cancel all further instances of that,
	/// also.
	///
	/// Will return an error if the `address` is invalid.
	///
	/// NOTE: This guaranteed to work only *before* the point that it is due to be executed.
	/// If it ends up being delayed beyond the point of execution, then it cannot be cancelled.
	///
	/// NOTE2: This will not work to cancel periodic tasks after their initial execution. For
	/// that, you must name the task explicitly using the `Named` trait.
	fn cancel(address: Self::Address) -> Result<(), ()>;

	/// Reschedule a task. For one-off tasks, this dispatch is guaranteed to succeed
	/// only if it is executed *before* the currently scheduled block. For periodic tasks,
	/// this dispatch is guaranteed to succeed only before the *initial* execution; for
	/// others, use `reschedule_named`.
	///
	/// Will return an error if the `address` is invalid.
	fn reschedule(
		address: Self::Address,
		when: DispatchTime<BlockNumber>,
	) -> Result<Self::Address, DispatchError>;

	/// Return the next dispatch time for a given task.
	///
	/// Will return an error if the `address` is invalid.
	fn next_dispatch_time(address: Self::Address) -> Result<BlockNumber, ()>;
}

/// A type that can be used as a scheduler.
pub trait Named<BlockNumber, Call, Origin> {
	/// An address which can be used for removing a scheduled task.
	type Address: Codec + Clone + Eq + EncodeLike + sp_std::fmt::Debug;

	/// Schedule a dispatch to happen at the beginning of some block in the future.
	///
	/// - `id`: The identity of the task. This must be unique and will return an error if not.
	fn schedule_named(
		id: Vec<u8>,
		when: DispatchTime<BlockNumber>,
		maybe_periodic: Option<Period<BlockNumber>>,
		priority: Priority,
		origin: Origin,
		call: Call,
	) -> Result<Self::Address, ()>;

	/// Cancel a scheduled, named task. If periodic, then it will cancel all further instances
	/// of that, also.
	///
	/// Will return an error if the `id` is invalid.
	///
	/// NOTE: This guaranteed to work only *before* the point that it is due to be executed.
	/// If it ends up being delayed beyond the point of execution, then it cannot be cancelled.
	fn cancel_named(id: Vec<u8>) -> Result<(), ()>;

	/// Reschedule a task. For one-off tasks, this dispatch is guaranteed to succeed
	/// only if it is executed *before* the currently scheduled block.
	fn reschedule_named(
		id: Vec<u8>,
		when: DispatchTime<BlockNumber>,
	) -> Result<Self::Address, DispatchError>;

	/// Return the next dispatch time for a given task.
	///
	/// Will return an error if the `id` is invalid.
	fn next_dispatch_time(id: Vec<u8>) -> Result<BlockNumber, ()>;
}